1. Field of the Invention
Exemplary aspects of the present invention relate to a fixing device and an image forming apparatus, and more particularly, to a fixing device for fixing a toner image on a recording medium, and an image forming apparatus including the fixing device.
2. Description of the Related Art
Related-art image forming apparatuses, such as copiers, facsimile machines, printers, or multifunction printers having at least one of copying, printing, scanning, and facsimile functions, typically form an image on a recording medium according to image data. Thus, for example, a charger uniformly charges a surface of an image carrier; an optical writer emits a light beam onto the charged surface of the image carrier to form an electrostatic latent image on the image carrier according to the image data; a development device supplies toner to the electrostatic latent image formed on the image carrier to make the electrostatic latent image visible as a toner image; the toner image is directly transferred from the image carrier onto a recording medium or is indirectly transferred from the image carrier onto a recording medium via an intermediate transfer member; a cleaner then cleans the surface of the image carrier after the toner image is transferred from the image carrier onto the recording medium; finally, a fixing device applies heat and pressure to the recording medium bearing the toner image to fix the toner image on the recording medium, thus forming the image on the recording medium.
The fixing device used in such image forming apparatuses may include a flexible, endless fixing belt faulted into a loop and a resistant heat generator provided inside the loop formed by the fixing belt to heat the fixing belt, to shorten a warm-up time or a time to first print (hereinafter also “first print time”). Specifically, the resistant heat generator faces the inner circumferential surface of the fixing belt across a slight gap through which radiation heat generated by the resistant heat generator is transmitted to the fixing belt quickly. A pressing roller presses against a nip formation member also provided inside the loop formed by the fixing belt via the fixing belt to form a nip between the fixing belt and the pressing roller through which the recording medium bearing the toner image passes. As the recording medium bearing the toner image passes through the nip, the fixing belt heated by radiation heat generated by the resistant heat generator and the pressing roller apply heat and pressure to the recording medium to fix the toner image on the recording medium.
With the above configuration, the slight gap provided between the resistant heat generator and the fixing belt prevents wear of the resistant heat generator and the fixing belt while at the same time providing the shortened warm-up time and the shortened first print time described above. Accordingly, even when the fixing belt rotates at a high speed, the resistant heat generator heats the fixing belt to a desired fixing temperature with reduced wear of the fixing belt and the resistant heat generator.
However, the fixing device including the resistant heat generator and the fixing belt has a drawback in that the flexible fixing belt may partially contact the resistant heat generator as the fixing belt rotates because there is only a slight gap between the resistant heat generator and the fixing belt to transmit heat from the resistant heat generator to the fixing belt effectively. Accordingly, a part of the fixing belt that contacts the resistant heat generator is exposed to excessive heat from the resistant heat generator. In other words, the fixing belt is not heated uniformly, resulting in uneven temperature distribution over the fixing belt.
Moreover, rotation and vibration of the pressing roller repeatedly applies mechanical stress to the resistant heat generator via the fixing belt, which bends the resistant heat generator. The repeated bending of the resistant heat generator causes fatigue failure and concomitant breakage or disconnection of the wiring of the resistant heat generator, resulting in faulty heating of the fixing belt.